COMBINED WITH WATERTON LAKES, its sister park just across Canada's border, Glacier offers more than 700 miles of foot trails, 48 glaciers, 1,600-odd miles of river and stream, 650 lakes, soaring peaks, hanging valleys, meadows spattered with wildflowers, thick evergreen forests, and several species that outrank you on the food chain. In short, it's a theme park for BACKPACKING. To find a chunk of backcountry all to yourself, the three-night, 20-mile Gunsight Pass Trail can't be beat. You'll trek through the guts of the park's wildernessone of North America's largest intact ecosystemswith killer mountain-and-lake ambience, a Continental Divide crossing, probable sightings of mountain goats, and possible encounters with grizzlies (be prepared). Leave your car at Lake McDonald on Glacier's west side, and take a park shuttle on 52-mile Going-to-the-Sun Road to Jackson Glacier Overlook, east of the Divide. Hike downvalley and then up from there, passing avalanche slopes and two glaciers, 6.2 miles along a drainage to Gunsight Lake, where you'll pitch a tent and bask in celestial views of Mount Jackson and Fusillade Mountain. Day two calls for a challenging five-mile leg over the Divide at 6,946-foot Gunsight Pass to Lake Ellen Wilson; up top, take time to poke around the old rock shelter, the only one remaining atop Glacier's passes. Day three is a short haul, "but the longest 2.7 miles in the park," says Glacier wilderness manager Kyle Johnson: a 1,120-foot gain to Lincoln Pass, followed by a 450-foot drop into Sperry Basin. Take your pick here: Pitch a tent at Sperry campground, or upgrade to a fairly pricey bunk nearby at the 1912 Sperry Chalet ($150 for the first person, $100 for each additional person, meals included; 888-345-2649, www.sperrychalet.com). Day four: six miles down, out of the subalpine zone, and into a forest of spruce, cedar, and hemlock to Lake McDonald.
WHEN TO GO: Many backcountry campsites, like Sperry, can't be advance-booked until August 1, when summer (all five weeks of it) reaches the park. But if the snow clears early, walk-ins can sometimes score a coveted berth in July. Pre-snowmelt in the high country, you need crampons, an ice ax, and glacier know-how so you don't Enron off a sheer drop-off into the abyss.
ANNUAL VISITORS: 1.73 million. (High: August, 487,800. Low: December, 3,387.)
MORE CHOICE ADVENTURE: RAFT the untamed, bouldery Middle Fork of the Flathead or the slightly more subdued North Fork (each Class II-IV), tinted emerald by glacial silt; BIKE Going-to-the-Sun by moonlight (east-to-west is the somewhat kinder direction).
HEADLAMP READING: Along the Trail: A Photographic Essay of Glacier National Park and the Northern Rocky Mountains, by Danny On and David Sumner; Man in Glacier, by C.W. Buchholtz
LOCAL SPECIALTY: Stop for huckleberry ice cream and Flathead cherries at any of the roadside stores on the way to the park. And the Park Cafe in St. Mary, Montana, makes ice cream and berry pies someone should write a song about.
INSIDE SCOOP: Need some incentive to brush up on bear etiquette? How about this: Since the park's establishment, grizzlies have killed ten people within its boundaries.
PARK HEADQUARTERS: 406-888-7800, WWW.NPS.GOV/GLAC